MTI LS-1 Engine Build - Tri-Power 427

MTI's dependable, powerful, and driveable LS1 Part 1

Step By Step

The foundation for all of that power is the aluminum Gen. III cylinder case. Thanks to GM's radical departure from the standard block design, all that is needed to increase the bore size on one of these beauties is a larger cylinder sleeve--and some ingenuity.

GM never intended for the Gen. III block to be bored, and the upper areas of the cylinder bore are extremely thin to allow coolant to pass between them. This is a factory LS6 block that was bored to 4.275-inch, and these holes in the case are commonplace.

Here, Pecos points out one of the factory block's shortcomings: the way the sleeves are put in, which involves casting the block around them, isn't always accurate. The machining on an LS1/LS6 has the closest tolerances of any GM block ever made, but the method of putting the sleeves in and casting around them makes for wall thicknesses that aren't the same all the way around.

Big horsepower, high reliability, and stock-like driveability--in order, those three parameters define the ultimate daily driven street engine. Each are, of course, highly desirable in a street car, and each is fairly easy to accomplish individually. So how is it that three simple characteristics can become so complicated when they're combined?

Even in this day of digitized keystroke tuning, only a select few wicked-fast street GMs possess these three attributes. It doesn't matter if it's big inches, big boost, or a nitrous motor--chances are that there's a spiky power curve here and an all-or-nothing rpm range there. And sometimes, there are parts everywhere.

Contrary to popular belief, the six-bolt-main-equipped LS1 and LS6 is prone to the same shortfalls that lesser GM mills suffer from--and in certain areas, more. Sure, it was both strong and powerful when it was nestled into the F- and Y-body platforms. But the high-tech sleeved cylinder case, a wonder when it is kept near-stock, has its own unique set of problems when the dyno line heads north. And for pure power output, even the mighty Gen. III is subject to the "no replacement for displacement" rule. 346 naturally aspirated inches get issues when 450 emissions-legal horses hit the pavement. Heading down the supernaturally aspirated road means much higher power outputs, as well as considering a forged crank and pistons set in place of the nodular iron and hypereutectic stockers. And therein lies the rub: Once that stock-displacement head/cam LS1 is all out of steam, making serious power live on the street gets to be a serious challenge.

Houston, Texas-based Motorsport Technologies is up for that challenge, which is very good news for you. Proprietor Jayson Cohen and his staff have spent the last 10 years producing some of the fastest Camaros, Firebirds, and Corvettes in the country, and Jayson soon noticed that the stock-cube LS1s could only breathe so hard. Extensive research and development time was spent to bore and stroke the LS1/LS6 cylinder case to 427 cubic inches--providing 50-plus more horsepower than the wildest heads/cam Gen. III, along with stock-like manners and longevity. The idea was to create a quick-revving, big-inch motor that would make 500-plus ponies, with enough low-end left over to get you around town.

"Depending on the customer's cam and exhaust system selections, 525 horsepower and around 500 ft.-lbs. of torque at the tires is within easy reach of this motor," Cohen explains. "Some of our customers who don't like to show their hand about how much is under the hood simply go with a quieter muffler and a smaller cam, for around 480 horses at the wheels."

MTI converts regular LS1s into 427-inch strokers at the rate of two a week. Around 50 percent of these mills are sent out mail-order; In addition to all of the happy Americans, customers as far away as Kuwait, Australia, and Norway have reaped the benefits of big-inch Gen. III power. GMHTP was interested in what it took to transform a 346-inch motor into a big-inch 427, and Pecos Loughlin, MTI's head machinist, gave us the guided tour. If you're ready to go big, follow along.

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